This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described below. However, it should be understood that these statements are to be read in light of this disclosure, and not as admissions of prior art.
Water-gas shift conversion reactions have been known for many years as a method of producing hydrogen and CO2 from carbon monoxide and steam. When little or no sulfur-containing compounds are present in the water-gas shift feed stream, this reaction is often referred to as a “sweet gas shift” reaction. Many catalytic materials have been used for the sweet gas shift reaction. For example, hydrogen can be prepared by passing carbon monoxide and steam over nickel or cobalt on a refractory porous material. Another common water-gas shift catalyst comprises copper oxide-zinc oxide. Another alternative water-gas shift catalyst utilizes iron oxide-chromium oxide.
Unfortunately, these catalysts do not tolerate small quantities of sulfur in the feed. As coal, coke and heavy hydrocarbon feeds suitable for conversion to hydrogen generally contain appreciable quantities of sulfur or sulfur containing compounds, such feeds can not be used with conventional water-gas or sweet gas shift catalysts.
Because of the increasing shortage of sulfur-free feed stocks and the increasing availability of feed stocks containing relatively high percentages of sulfur compounds, sometimes referred to as “sour gas feeds”, the need has become apparent for the development of carbon monoxide water-gas shift catalysts which can operate effectively in feed streams containing more than a nominal quantity of sulfur or sulfur-containing materials. This reaction is referred to as a “sour gas shift” reaction (“SGS”).
Various types of catalysts have been proposed for use in these sulfur containing feeds for sour gas shift reactions, particularly catalysts containing a combination of cobalt or nickel and molybdenum or tungsten. It is known that oxide catalysts made from these materials must be converted to their corresponding sulfided state to permit reasonable activity. In fact, in sour gas shift reactions, sulfur or sulfur containing compounds are required to be present in the feed stream or the sour gas shift catalyst will be deactivated. Accordingly, it is necessary to perform a sulfidation reaction, sometimes referred to as a sulfurization or presulfurization reaction, on the precursor sour gas shift catalysts prior to their utilization as sour gas shift catalysts in a feed containing sulfur or sulfur containing compounds. This sulfidation process can occur in situ or ex-situ with sulfidation occurring at a separate location or facility than the location at which the sour gas shift reaction occurs being preferred.
The process for sulfidation of sour gas shift catalysts has not been studied in depth. In the past, this sulfidation reaction has typically been conducted on precursor sour gas shift catalysts using the same sulfidation processes utilized for sulfidation of catalysts used for hydrotreating, hydrocracking or hydroconversion. Typically, “hydrotreating” refers to converting organic sulfur or nitrogen to hydrogen sulfide or ammonia in the presence of hydrogen. “Hydrocracking” refers to the treatment of heavy fuel fractions to convert them to lighter fractions, such as gasoline, jet fuels and gas oils. “Hydroconversion of hydrocarbons” refers to hydrocarbon (olefin) saturation during the process of hydrotreating. Co (Ni)—Mo (W)/carrier based catalysts, which are commonly used for hydrotreating and/or hydroconversion of hydrocarbons, can be sulfided in-situ or ex-situ utilizing sulfur containing compounds. Typical sulfidation conditions for these reactions utilize a wide range of S/H2 ratios (0.03/1 to 20/1) and temperatures (200 to 600 C). However, the preferred sulfidation temperature is 300 to 400 C. There are no accepted limitations on the acceptable ratio of S/H2 for the sulfidation of the catalysts for these reactions, regardless of the temperature of the feed stream.
In contrast to hydrotreating, hydrocracking and hydroconversion reactions, the sour gas shift reaction is a reaction whereby carbon monoxide and steam are converted into carbon dioxide and hydrogen in the presence of sulfur compounds.
Although processes for the sulfidation of sour gas shift catalysts based on sulfidation procedures utilized for these other reactions have been employed, there are no recognized procedures that have been accepted specifically for sour gas shift catalyst sulfidation. Thus, there is a need for analysis and improvement in the process for the sulfidation, specifically for sour gas shift catalysts.